The present invention relates to a reproduction power control method, a reproduction power control device, and a record reproducing device incorporating the same, capable of scanning a recording mark using a light beam, shone on the recording medium, of which beam the power is optimally controlled.
Efforts have been put in recent years to increase data storage density on magneto-optical disks, and approaches have been proposed to scan recording marks smaller in diameter than a light beam spot.
Japanese Laid-open Patent Application 5-81717 (Tokukaihei 5-81717; published on Apr. 2, 1993) discloses one of such approaches, a superresolution magneto-optical disk and its recording method.
According to the recording method, a magneto-optical recording medium containing a recording layer and a reproduction layer exhibiting in-plane magnetization is used, and a light beam is shone onto the reproduction layer side of the medium. The reproduction layer is thereby partially heated where it is hit by the light beam. As the temperature of those parts (aperture) of the reproduction layer rises exceeding a predetermined value, the parts come to exhibit vertical magnetization because of the copying of magnetism onto them from the corresponding parts of the recording layer due to internal magnetization. Thus, the recording marks which are smaller in diameter than the spot made by the light beam can be scanned.
However, the optimal reproduction power of a light beam changes depending on variations of temperature and other environmental conditions. (Note that the optimal reproduction power of a light beam is defined as a reproduction power of a light beam which is controlled to produce a reproduction signal with sufficient output power for data reproduction and to keep such the size of the aperture that best minimizes crosstalk (noise) signals.) Therefore, in some cases, the reproduced data is not so reliable as it should be, even when the reproduction power of the light beam is kept constant during the reproduction.
More specifically, suppose that the current reproduction power is greater than the optimal reproduction power, the aperture grows greater than the recording mark and covers recording marks in an adjacent track and those that are adjacent with respect to the tangential of the track, thereby causing interference to occur between adjacent bits. In other words, the power of the reproduction signal (crosstalk signal) from the adjacent track and the recording marks that are adjacent with respect to the tangential of the track increases and interferes, in other words, produces an overlapping reproduction waveform. This reduces the amplitude in high frequency range and degrades the S/N ratio, thus rendering read errors more likely to occur.
On the other hand, if the current reproduction power is less than the optimal reproduction power, the aperture grows small. Under these circumstances, although the ratio grows larger of the amplitude in high frequency range to the amplitude in low frequency range, detection is in practice done using only a central part of the light beam, reducing the rate of the signal contained in reflection light and overall amplitude. This reduces the power of the reproduction signal from the target track. Therefore, the S/N ratio degrades and renders read errors more likely to occur.
Accordingly, Japanese Laid-open Patent Application 8-63817 (Tokukaihei 8-63817; published on Mar. 8, 1996 and corresponding to U.S. Pat. No. 5,617,400) describes a record reproducing device capable of keeping an optimal reproduction power using recording marks of differing lengths. The record reproducing device detects the signal levels of the readout signals from the recording marks of differing lengths and controls the reproduction power of a light beam based on comparison between the signal levels of detected signals corresponding to the recording marks.
However, the record reproducing device described in Japanese Laid-open Patent Application 8-63817 requires the provision of an area to record several sets of patterns of different lengths on a recording medium, separately from recorded data. The provision accordingly reduces the user area on which the user can record and/or reproduce information.
A principal objective of the present invention is to offer a reproduction power control method, a reproduction power control device, and a record reproducing device incorporating the same, capable of reproduction power control without reducing the user area on a recording medium.
In order to solve the aforementioned problems, a reproduction power control device in accordance with the present invention is a reproduction power control device, for use in a record reproducing device which reads recorded information by shining a light beam onto a recording medium, for controlling a reproduction power of the light beam, and includes:
adapting/equalizing means for equalizing a reproduction signal corresponding to the recorded information obtained from the recording medium by shining the light beam to a predetermined frequency characteristic; and
reproduction power control means for, based on an equalization amount in the equalization, detecting an error between a current reproduction power and an optimal reproduction power and controlling the reproduction power of the light beam so as to bring the error closer to 0.
A reproduction power control method in accordance with the present invention includes:
the equalization amount computing step of computing an equalization amount from an equalization coefficient used when adapting and equalizing a reproduction signal obtained by shining a light beam onto a recording medium; and
the reproduction power altering step of comparing a current reproduction power and an optimal reproduction power by comparing the equalization amount with an optimal equalization amount prespecified to a predetermined value, so as to control a drive current for a light source emitting the light beam based on a result of the comparison.
Here, the optimal reproduction power refers to a reproduction power of a light beam which is controlled to produce a reproduction signal with sufficient output power for reproduction of recorded information and to keep such the size of the aperture that best minimizes crosstalk (noise) signals.
The equalization amount refers to the deviation of the frequency characteristic of the reproduction signal off a desired frequency characteristic.
According to the arrangement or method, the reproduction power of a light beam can be controlled by computing the equalization amount and controlling the drive current based on the equalization amount.
Therefore, for example, there is no need to provide special areas on the recording medium where long and short marks or otherwise arranged marks to control reproduction power are recorded, thus enabling reproduction power control without reducing the user area (area on which the user can record and/or reproduce information) on the recording medium.
A record reproducing device in accordance with the present invention includes:
a light source; and
a reproduction power control device including: adapting/equalizing means for equalizing a reproduction signal corresponding to recorded information obtained from a recording medium by shining a light beam to a predetermined frequency characteristic; and reproduction power control means, for based on an equalization amount in the equalization, detecting an error between a current reproduction power and an optimal reproduction power and controlling a reproduction power of the light beam so as to bring the error closer to 0,
wherein
the information recorded on the recording medium is reproduced whilst the reproduction power control device is controlling the reproduction power of the light beam emitted from the light source onto the recording medium.
According to the arrangement, there can be provided a reproduction power control device capable of optimally controlling a reproduction power. Therefore, a record reproducing device can be offered which boasts high reliability in reproduced data.
In order to solve the aforementioned problems, another reproduction power control device in accordance with the present invention is a reproduction power control device, for use in a record reproducing device which reads recorded information by shining a light beam onto a recording medium, for controlling a reproduction power of the light beam, and includes:
equalizing means for equalizing a reproduction signal corresponding to the recorded information obtained from the recording medium by shining the light beam and detecting an error between an equalized frequency characteristic and a predetermined frequency characteristic; and
reproduction power control means for, based on the error, detecting an error between a current reproduction power and an optimal reproduction power and controlling the reproduction power of the light beam so as to bring the error closer to 0.
Another reproduction power control method in accordance with the present invention includes:
the update amount computing step of computing an update amount for an equalization coefficient based on a predetermined coefficient used when equalizing a reproduction signal obtained by shining a light beam onto a recording medium;
the equalization amount computing step of computing an equalization amount from the update amount for the equalization coefficient; and
the reproduction power altering step of comparing a current reproduction power with an optimal reproduction power by comparing the equalization amount with an optimal equalization amount prespecified to a predetermined value, so as to control a drive current for a light source emitting the light beam based on a result of the comparison.
According to the arrangement or method, by equalizing the reproduction signal using the equalizing means and detecting an error (equalization coefficient update data) between the equalized frequency characteristic and the predetermined frequency characteristic (initial value of the equalization amount), the reproduction power of a light beam can be controlled based on that error.
In other words, the equalization amount is computed based on the update amount of the equalization coefficient computed using a predetermined coefficient and compared with an optimal equalization amount.
In this manner, the light beam power can be controlled so as to obtain a desired impulse response at the predetermined initial value of the equalization amount. Hence, the reproduction power can be appropriately controlled.
Therefore, for example, reproduction power control is possible without providing special areas on the recording medium where long and short marks or otherwise arranged marks to control reproduction power are recorded, thus enabling reproduction power control without reducing the user area (area on which the user can record and/or reproduce information) on the recording medium.
Another record reproducing device in accordance with the present invention includes:
a light source; and
a reproduction power control device including: equalizing means for equalizing a reproduction signal corresponding to recorded information obtained from a recording medium by shining a light beam and detecting an error between an equalized frequency characteristic and a predetermined frequency characteristic; and reproduction power control means for, based on the error, detecting an error between a current reproduction power and an optimal reproduction power and controlling a reproduction power of the light beam so as to bring the error closer to 0,
wherein
the information recorded on the recording medium is reproduced whilst the reproduction power control device is controlling the reproduction power of the light beam emitted from the light source onto the recording medium.
According to the arrangement, there can be provided a reproduction power control device capable of optimally controlling a reproduction power. Therefore, a record reproducing device can be offered which boasts high reliability in reproduced data.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.